This continuation grant proposes: 1. To study the structure of peroxidase Compound I and Compound X and to relate the structures of the intermediates to enzyme catalysis, especially in the area of biological halogenation reactions. 2. To study the mechanism of activation of pyruvate oxidase by phospholipids and other amphiphilic molecules. The catalytic activity of pyruvate oxidase can be enhanced 25 to 100 fold by the binding lipid activators to the enzyme. 3. To continue our studies on the activation of endonuclease I by colicin E2.